Yep, just solve all the puzzles within 2 miles of where you want to hide your cache - but seriously, there is no other way to know.

I had that same thought ... but couldn't solve the first puzzle I tried!

Been there many times! Try asking the CO for a hint (most are willing to help) and if that doesn't work, see if a previous finder will give you a bump to get you going. Watch out though, once you start solving puzzles, you might get hooked!